River Otter Management in Pennsylvania - PA Game ...
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
River Otter Management in Pennsylvania
(2013-2022)
prepared by
Tom Hardisky
Wildlife Biologist
Pennsylvania Game Commission
* Draft *
April 2013
This plan was prepared and will be implemented at no cost to Pennsylvania taxpayers. The Pennsylvania Game
Commission is an independently-funded agency, relying on license sales, State Game Land timber, mineral, oil/gas
revenues, and federal excise taxes on sporting arms and ammunition. The Game Commission does not receive any
state general fund money collected through taxes. For over 100 years, sportsmen and women have funded game,
non-game, and endangered species programs involving birds and mammals in Pennsylvania. Hunters and trappers
continue to financially support all of Pennsylvania’s wildlife programs including river otter management.
EXECUTIVE SUMMARY
While information on the historic distribution of North American river otters in Pennsylvania is
limited, otters were likely found in every major watershed in the state during the late 1800s. The
combined effects of habitat destruction, water pollution, and unregulated harvest caused the
extirpation of river otters from most of Pennsylvania by the early to mid-1900s. Restoration
efforts began in 1982, leading to successful population recovery. Pennsylvania otter populations
have been protected and have increased for more than 30 years after otter restoration was
initiated. Like otter restoration, otter management will ensure that populations remain healthy
and self-sustaining for the benefit all Pennsylvanians.
The purpose of this plan is to provide an overview of the current state of knowledge pertaining to
river otter biology, habitat, history, resource value, and population management and provide
direction for future management. It represents our guide to managing otter populations in
Pennsylvania for the next 10 years. It also serves as an information and education resource for
anyone seeking answers to questions concerning river otter life history and past, present, and
future otter management in the Commonwealth.
Objectives defined in the plan identify the necessary steps to achieve each of the four goals.
Strategies consisting of actions and research needs were developed to attain each objective.
Improved population and reproductive monitoring, harvest management, habitat assessment,
population management, trapping regulations, damage management, outreach, and public
engagement are among the most important needs identified.
In keeping with our agency mission, river otters must be managed for the benefit of other
wildlife species, their habitats, and all Pennsylvanians for generations to come. Our otter
management mission is to maintain stable otter populations in balance with their habitat for the
benefit of other wildlife species and humans through proper monitoring, population
management, and damage control. The goals of Pennsylvania’s river otter management are to (1)
maintain sustained otter populations within suitable habitat, (2) minimize otter damage
complaints, (3) increase public awareness and knowledge of the benefits of otters and their
habitat, and (4) develop guidelines to assess river otter harvest feasibility and implement a
harvest management program.
Pennsylvania’s otter management plan provides the necessary direction to achieve enhanced
populations, habitat, and monitoring, increased public awareness and knowledge of otters, and
sustained resource opportunities for both consumptive and non-consumptive users of this
valuable furbearer. Only through careful planning and sound science will we maintain a healthy
balance between otters and human interests, and manage sustained river otter populations for
future generations.
2
MISSION, GOALS, OBJECTIVES, AND STRATEGIES
Mission: Maintain river otter populations in balance with their habitat through proper population
monitoring and harvest management.
GOAL 1. Maintain sustained river otter populations within suitable habitat.
Objective 1.1. Annually monitor statewide river otter status, distribution, and population trends.
Strategies
1.1.1. Determine population status and distribution using annual furbearer survey
results or other method.
1.1.2. Monitor population trends based on relative abundance estimates from
annual furbearer surveys or other method.
Objective 1.2. Develop a statewide river otter population monitoring program to estimate
population levels.
Strategies
1.2.1. Establish a direct-census method of determining population levels such as
mark-recapture to achieve a high level of accuracy.
1.2.2 Determine population estimates for each WMU.
1.2.3. Establish a census protocol to monitor future population changes.
Objective 1.3. Develop a model to monitor population changes within each WMU or other larger
unit.
Strategies
1.3.1. Estimate age- or age class-specific litter size and female reproductive
potential.
1.3.2. Estimate age- or age class-specific mortality from incidental mortality or
future harvest.
1.3.3. Estimate age- or age class-specific survival.
Objective 1.4. Develop a geographic information system river otter habitat suitability model for
Pennsylvania.
3
Strategies
1.4.1. Identify and map suitable waterways for river otter occupancy.
1.4.2. Map unoccupied, but potential river otter habitat.
Objective 1.5. Manage river otter populations on public and private land for maximum wildlife
benefit.
Strategies
1.5.1. Integrate river otter habitat needs into the public lands planning process.
1.5.2. Provide information and assistance to private landowners to improve river
otter habitat on their lands.
GOAL 2. Minimize river otter damage complaints.
Objective 2.1. Evaluate the frequency and extent of river otter damage complaints annually.
Strategy
2.1.1. Annually survey agency staff to obtain the number of otter damage
complaints received and information on type of damage.
Objective 2.2. Assess the need for public outreach and engagement regarding otter damage.
Strategy
2.2.1. Conduct a survey to determine the public’s knowledge of otters and
options for damage control as well as the public’s desired otter population
level.
2.2.2. Provide technical assistance to the public to prevent or reduce otter
damage.
GOAL 3. Increase public awareness and knowledge of river otters.
Objective 3.1 Increase public awareness of river otter life history, population origins, and
conservation significance in Pennsylvania.
Strategies
3.1.1 Develop a PowerPoint presentation describing river otter life history,
conservation significance, and management in Pennsylvania.
4
3.1.2 Develop a brochure or electronic document describing the role of harvest
management in maintaining a balance between otter numbers and prey
resources and make it accessible through the PGC website and social
media.
Objective 3.2. Develop river otter viewing opportunities and guidelines to locate otter sign.
Strategy
3.2.1. Provide guidelines to the public on how to increase chances of seeing an
otter and locating otter sign.
GOAL 4. Develop guidelines to assess river otter harvest feasibility and implement a
harvest management program.
Objective 4.1. Assess impacts of various harvest strategies on otter populations.
Strategies
4.1.1. Assess harvest feasibility for each WMU based on population level and
habitat suitability.
4.1.2. Model affects of various harvest levels on WMU-based population
objectives.
Objective 4.2. Develop river otter harvest management recommendations to achieve WMU
population objectives.
Strategy
4.2.1. Establish an annual regulated trapping season for otters in WMUs with
adequate population levels.
4.2.2. Reinforce or provide guidelines on how to avoid an otter capture to
trappers in WMUs closed to otter trapping.
4.2.3. Develop an otter management decision matrix based on population and
habitat status information to help guide regulatory action or response.
5
TABLE OF CONTENTS
Executive summary......................................................................................................................... 2
Mission, Goals, Objectives, and Strategies ..................................................................................... 3
SECTION 1: Biology...................................................................................................................... 7
Taxonomy ................................................................................................................................... 7
Distribution ................................................................................................................................. 7
Physical description .................................................................................................................... 8
Reproduction and development .................................................................................................. 9
Mortality ................................................................................................................................... 10
Food habits and foraging behavior ........................................................................................... 11
Social organization, spatial distribution, and behavior ............................................................. 13
Habitat ....................................................................................................................................... 15
SECTION 2: Historic and Current Status in Pennsylvania .......................................................... 17
Historic status............................................................................................................................ 17
Population recovery .................................................................................................................. 17
Population monitoring .............................................................................................................. 18
Current status and distribution .................................................................................................. 21
SECTION 3: Resource and Economic Values.............................................................................. 23
Resource value .......................................................................................................................... 23
Damage management ................................................................................................................ 23
SECTION 4: Population Management ......................................................................................... 25
Management approaches ........................................................................................................... 25
Population and harvest management ........................................................................................ 25
Population monitoring .......................................................................................................... 26
Harvest monitoring ............................................................................................................... 27
Population growth ................................................................................................................. 28
Aging techniques .................................................................................................................. 29
Management guidelines for Pennsylvania ................................................................................ 29
Plan implementation ................................................................................................................. 33
Literature Cited ............................................................................................................................. 36
Appendix 1. Annual furtaker mail survey.................................................................................... 46
Appendix 2. Annual Wildife Conservation Officer furbearer questionnaire. .............................. 47
Appendix 3. U.S. Fish and Wildlife Service memorandum on river otter export ....................... 49
Appendix 4. River otter population and harvest monitoring methods. ........................................ 50
Appendix 5. Objective and supporting strategy completion timetable. ....................................... 52
Appendix 6. Summary of public comments. ............................................................................... 56
6SECTION 1: BIOLOGY
Taxonomy
Two species of river otters are recognized in the world. The Nearctic river otter (Lontra
canadensis) is a member of the Order Carnivora, Family Mustelidae, and Genus Lontra. The
similar-looking Neotropical river otter (L. longicaudis) is found in portions of Europe and Asia.
River otter taxonomy has been problematic throughout much of its early history. Newly-
described taxa were based on differences in gender, age, molt stage, and pelt condition and led to
confusion among scientists’ species and subspecies descriptions (Melquist et al. 2003). Based on
phylogenetic data analysis, Van Zyll de Jong (1987) separated Old World (Eurasian) from New
World (Nearctic) otters and concluded that Nearctic otters originated in Eurasia and spread
southward from the Bering Land Bridge across North America and the Panamanian Land Bridge.
He also recognized Neotropical river otters as a distinct species.
Hall and Kelson (1959) recognized 19 subspecies of river otters in North America. Many other
variations in subspecies divisions have been proposed. Common names for river otters in North
America include northern river otter, Canadian otter, land otter, and fish otter (Toweill and Tabor
1982). In the literature, the scientific name for the North American river otter was Lutra
canadensis prior to 1998. In 1998, Koepfli and Wayne (1998) found that genetic separation
between new and old world otters was significant enough to be considered separate genera.
Scientists gradually adopted this change over the next 10 years. Lontra canadensis is accepted as
proper nomenclature for this species. Both scientific names refer to the same species, sometimes
creating confusion in the literature.
Distribution
Prior to European settlement, river otters ranged
throughout most of the North American continent.
Otters were found in all major waterways until at
least 1800. Human development and habitat
changes were undoubtedly responsible for
extirpation from some portions of their range. Over
harvest in some areas may have resulted in local
extirpation. In 1977, 71% of the otter’s historical
range was occupied (Deems and Pursley 1978). By
1998, 90% of the otter distribution during
European settlement was filled (Fig. 1; Melquist et
al. 2003).
Today, river otters are associated with waterways ● introduction/restocking site verified reports
and wetlands throughout North America. The Fig. 1. North American distribution of river otters in
primary barriers to dispersal are arid regions of 1998 depicted by shaded area (Melquist et al. 2003).
southwestern North America. Mountain ranges and
salt water areas can limit dispersal, but do not represent insurmountable barriers to movement
7(Magoun and Valkenburg 1977). The future of wetlands and riparian areas is critical to the future
status and distribution of otters in North America.
Physical description
The river otter is adapted for both land and water. Its long, cylindrical body is shaped like a
torpedo reaching its greatest diameter at the thoracic region (Tarasoff et al. 1972). The head is
small, blunt, and flattened with a short, wide nose. Small ears provide acute hearing, are set well
back, and are closed off by anterior and posterior ridges during submersion (Pocock 1921). The
eyes are small and set high on the head on a similar plane with the ears, enabling otters to swim
low in the water. Otters are nearsighted, an adaptation for underwater vision. Their vision is not
acute, but they can detect movement at considerable distances (Toweill and Tabor 1982). Tactile
senses in river otters are highly developed. An otter’s highly-sensitive whiskers behind and
below the nose aid it in locating and capturing prey in murky, turbid waters and during dark
nights (Melquist and Hornocker 1983). The neck is thick and rarely smaller in diameter than the
head (Toweill and Tabor 1982). Like many other mustelids (members of the weasel family),
otters have well-developed anal musk glands (Vaughan 1978). When frightened, these scent
glands release a pungent odor.
An otter’s legs are short, stocky, and powerful. The feet have five toes with inter-digital webbing
and well-developed, non-retractable claws. Hind feet have heel pads with four small, rough
protuberances for greater traction on slippery surfaces (Melquist and Dronkert 1987). An otter’s
tail accounts for about 40% of its body length (Melquist and Hornocker 1983) and is relatively
long, thick, pointed, and fully-furred.
Male river otters are approximately 17% larger than females of equal age. Length and weight
vary considerably among otter subspecies with a decrease in body size from north to south
(Toweill and Tabor 1982), but not from west to east (Van Zyll de Jong 1972). Adults weigh 11-
33 lbs (5-15 kg) with total lengths ranging from 35-54 in (89-137 cm) (Hall 1981). The average
weight of males is about 25 lbs (11.3 kg), while females average 19 lbs (8.6 kg) (Deems and
Pursley 1983). After 3-4 years of age, Stephenson (1977) found that maximum length is achieved
and adult females showed decreased weight after 4 years.
River otter teeth are adapted for grasping, shearing, grinding, and crushing. The dental formula is
incisors 3/3, canines 1/1, premolars 4/3, and molars 1/2, for a total of 36 teeth (Jones and
Manning 1992). Dentition is less massive than that of the sea otter (Enhydra lutris). Dental
anomalies, including extra premolars, have been reported (Dearden 1954), but do not appear to
affect survival.
An otter pelt consists of short, dense, soft underfur protected by longer, stiff, glossy guard hairs.
Air trapped within the thick underfur acts as insulation when underwater. The color of the dorsal
side ranges from rich, dark chocolate brown to pale chestnut. Ventrally, the color is light brown
to a silver gray. There is no significant pelage color variation between sexes, among ages, and
throughout seasons of the year. Fur length, density, and to some extent color are related to
climate. The more northern otters have the longest and thickest pelage (Van Zyll de Jong 1972).
8Southern and western otters tend to be lighter in color than those from the north and east
(Toweill and Tabor 1982).
Like other aquatic furbearers, river otters undergo only one molt each year during the summer
(Ling 1970, 1984). Soon after becoming prime, the tips of guard hairs tend to curl or become
“singed,” decreasing the value of the river otter pelt (Obbard 1987). Otter pelts are valued
because of their durability in garments. They are the standard against which other furs are rated
for durability (river otters = 100% durability) (Kaplan 1974).
Reproduction and development
River otter reproductive biology and development of the young is complicated, yet intriguing.
Male and female genitalia are typical of most mammals. Gender is evident even among
developing embryos (Polechla 1987). Males have a penis with an ossified baculum (os penis).
The penis is somewhat unique in vascularization and musculature among mustelids (Long 1969).
An adult male otter normally possesses a well-developed baculum. The baculum increases in
length until the male reaches about 3 years of age and increases in weight until about age 6
(Stephenson 1977). Testes fluctuate in size seasonally depending on level of development and
sperm production. Females may develop an os clitoridis as they mature. This structure is
cartilaginous in females less than 2 years of age, but may become ossified thereafter
(Lauhachinda 1978). The uterine horns of the female become more vascularized with age. Otters
have 4 mammae.
Both male and female otters do not reach sexual maturity until 2 years of age (Liers 1951,
Hamilton and Eadie 1964, Tabor and Wight 1977, Lauhachinda 1978). The breeding season is
typically spread over a 3-month period during late winter to early spring. The estrus period of the
female lasts 42-46 days with peak receptive periods occurring every 6 days (Liers 1951).
Receptive female otters may advertise their condition by marking at scent stations. Copulation
normally occurs in the water, but may also occur on land, lasting up to 25 minutes (McDaniel
1963). Otter may copulate several times a day and on consecutive days (Park 1971). Melquist
and Hornocker (1983) observed a radio-marked female copulating 3-4 weeks after she had given
birth. The time between reproductive cycles (birth to birth) is variable. Some researchers
reported annual reproduction in Oregon (Tabor and Wight 1977), Idaho (Melquist and
Hornocker 1983), and Arkansas (Polechla 1987). Biannual reproduction was observed in
Alabama and Georgia (Lauhachinda 1978) and Maryland (Mowbray et al. 1979). Reproduction
occurred in both 1- and 2-year cycles in Arkansas (Polechla 1987) and Wisconsin (Liers 1951).
River otters undergo the process of delayed implantation as part of their reproductive cycle.
Following conception, embryo development proceeds to the blastocyst stage. However, the
blastocyst stops development, does not implant into the uterine wall, and floats freely in the
uterus for an extended period. Photoperiod is the apparent trigger for hormonal control of the
implantation process (Melquist et al. 2003). Polechla (1987) found that implantation occurred
throughout river otter range when a photoperiod of approximately 10.5 hrs light: 13.5 hrs dark
was reached. Delayed implantation may have an evolutionary advantage. The timing of
implantation may coincide with upcoming energy-demanding reproductive events and periods of
abundant food availability (Polechla 1987).
9Because of delayed implantation, reported gestation periods vary considerably among
researchers. The exact duration of the inactive (unimplanted) and the active (implanted) stage of
pregnancy is unknown. Gestation periods ranging from 288-380 days have been reported (Liers
1951, Hamilton and Eadie 1964). River otters as well as other aquatic and semi-aquatic
mammals have the longest period of delay, averaging 274 days (Ferguson et al. 1996). Growth of
the embryo proceeds rapidly after implantation is complete (Huggett and Widdas 1951). The
active period of pregnancy is believed to last 60-63 days (Lancia and Hair 1983).
Prior to the birthing period, females normally retreat to a pond, lake, or small tributary stream
with adequate food, shelter, and isolation from disturbances. Natural shelters or burrows of other
animals are often used as natal dens. Natural as well as artificial rock cavities are also used. The
natal den is rarely used by the female and her offspring during other seasons (Melquist and
Hornocker 1983). Female otters generally do not use the same den each year.
Litter sizes of 1-6 have been reported. However, litters of 2-3 are most common (Melquist and
Dronkert 1987). Ovulation rates range from 2.4 to 3.0 eggs per female (Toweill and Tabor 1982).
Lauhachinda (1978) reported a slight increase in corpora lutea production (2.4 to 3.3) from age
3-6, and then a decline to an average of 3.0 per female for otters aged 7-15. Birth of litters may
occur from November through May. Peak parturition occurs during March and April across otter
range (Hamilton and Eadie 1964, Tabor and Wight 1977). Wide variation in the timing of
parturition is normal and may occur even within a local population.
Weighing about 4-6 ounces (120-160 g) at birth, newborn pups are black, blind, toothless, and
helpless (Melquist and Dronkert 1987). Lengths of newborns range from 8-11 inches (20-28 cm).
Otter milk has a high content of fat and protein, but is low in carbohydrates (Toweill and Tabor
1982). Pups grow rapidly on this diet and emerge from natal dens in 2 months. By 3 months, the
young are weaned and can travel well enough to leave the natal area with the female (Melquist
and Hornocker 1983). Adult males do not participate in rearing the young.
Mortality
Human activities cause the majority of river otter mortality. Habitat destruction and modification
are by far the most serious sources of mortality among otters. More direct mortality factors
include road accidents, accidental trapping, and trapping incidental to beaver harvest. Less
common mortality sources are predation, parasites, diseases, and disorders related to water
toxicity.
River otters are a relatively long-lived species. They have been known to live 14 years in the
wild (Lauhachinda 1978, Brown and Parsons 1983). A 10-15 year life is the estimated longevity
in the wild (Melquist and Dronkert 1987).
Habitat destruction, without exception, was the primary cause of the decline in otter numbers that
led to the extirpation from nine states and one Canadian province (Deems and Pursley 1978).
Habitat degradation and loss is represented in many forms. Lauhachinda (1978) attributed the
disappearance of otters from parts of West Virginia, Tennessee, and Kentucky to groundwater
10acidity due to mining operations. Other forms of otter habitat destruction include development of
waterways for economic or recreational benefit, destruction of riparian habitat for additional
farmland or building sites, and declines in water quality resulting in conditions such as increased
siltation or additions of pesticide residues or other toxins associated with intensive farming
practices (Melquist et al. 2003).
Because of the susceptibility of otters to pollution, this furbearer has been recognized as an
indicator species for environmental health of aquatic ecosystems (Melquist and Dronkert 1987).
Industrial pollutants, heavy metals, and chlorinated hydrocarbons undergo biomagnifications as
they move up the food chain (Halbrook et al. 1981). Accumulation of chemical compounds is a
serious threat to all upper trophic life forms, especially otters. Several recent studies have
monitored levels of pollutants such as mercury (Haines et al. 2010, Spencer et al. 2011) and
polychlorinated biphenyls (PCBs)(Grove and Henry 2008, Lemarchand et al. 2010) in otter
tissue. Some otter population declines have been directly linked to toxins such as PCBs (Henny
et al. 1981). Additive or synergistic effects of many pollutants are largely unknown.
Otters have few natural enemies. They are essentially safe from predators in the water, but are
vulnerable on land. Bobcats (Felis rufus), dogs, coyotes (Canis latrans), foxes, and alligators
(Alligator mississippiensis) have been identified as predators (Young 1958, Vallentine et al.
1972). Other predators such as mountain lions (Felis concolor), wolves (Canis lupus), black
bears (Ursus americanus), and large raptors likely kill otters on occasion (Rosen 1975, Toweill
and Tabor 1982). Most predation is directed toward young animals or adults traveling on land.
No natural predator has had a serious impact on otter populations (Toweill and Tabor 1982).
River otters are susceptible to a variety of viral, bacterial, fungal, and protozoan diseases
(Melquist et al. 2003). Canine distemper (Davidson 2006) and rabies (Serfass 1995) are among
the more common viral diseases reported. In general, little is known about diseases in free-
ranging otters.
A wide variety of ecto- and endoparasites are known to infect otters. Kimber and Kollias (2000)
summarized parasite reports for river otters. They found 11 species of ectoparasites (7 species of
tick, one sucking louse, one flea, and two species of beetle) and 36 species of helminth
endoparasites. Infection of the nematode Dracunculus lutrae has been reported by trappers
(Davidson 2006). The large white roundworms are coiled in the subcutaneous tissues and
occasionally found by trappers while skinning otters.
Trapper harvest of otters for their fur can have a direct impact on otter populations if taking is
unregulated. No state or Canadian province allowed unregulated harvest of river otters in recent
history.
Food habits and foraging behavior
River otters are primarily non-selective fish eaters and are regarded as specialists at catching
fish. Though their diet varies seasonally and regionally, the bulk of a river otter’s diet is
composed of fish. For the most part, crustaceans (primarily crawfish), reptiles, amphibians, birds,
insects, and mammals are of lesser importance.
11Otters normally take a wide variety of food items. However, certain patterns of fish vulnerability
are evident. Predation on fish is directly proportional to their availability and inversely
proportional to their swimming ability (Ryder 1955, Toweill 1974, Stenson et al.1984, Serfass et
al. 1990). Toweill and Tabor (1982) offered three general concepts associated with otter prey
selection: (1) otters do not select a particular species of fish when hunting, (2) slow-swimming
species of fish are more vulnerable than fast-swimming species, and (3) injured or weakened fish
are more vulnerable to otter predation than healthy, vigorous fish. Otters tend to select larger,
less maneuverable fish. Larger fish are less able to find effective cover than smaller fish.
Catchability is a key factor in prey selection. Feeding patterns of otters essentially target
abundant, slow-moving fish species that are selected more often than their abundance in the
watershed would indicate (Toweill and Tabor 1982). Examples include suckers (Catostomus sp.),
carp (Cyprinus sp.), chubs (Semotilus sp.), daces (Rhinichthys sp.), shiners (Notropis sp.), and
catfishes and bullheads (Ictalurus sp.). Fish species found in large schools such as sunfishes
(Lepomis sp.), darters (Etheostoma sp.), and perch (Perca sp.) are also important prey. Bottom-
dwelling fish, mudminnows (Umbra limi) and sculpins (Cottus sp.) for example, are particularly
susceptible to otter predation because of their habit of remaining immobile until a predator is
close. Fast-moving species like trout (Salmo sp.) and pike (Esox sp.) are taken by otters in lesser
quantities. Most researchers have reported these otter feeding patterns (Lagler and Ostenson
1942, Wilson 1954, Greer 1955, Ryder 1955, Sheldon and Toll 1964, Knudsen and Hale 1968,
Toweill 1974, Lauhachinda 1978, Serfass et al. 1990).
Other prey items including several species of crayfish are important in an otter’s diet. Several
researchers found that crawfish were the dominant food item during warmer months, while fish
were the primary food item during colder months (Roberts et al. 2008, DeKar et al. 2010, Stearns
and Serfass 2011). Based on prey availability, DeKar et al. (2010) found that otter consumption
represented a large fraction of prey production, indicating potentially strong effects of otters on
the trophic dynamics of stream ecosystems in Ontario, Canada. Reptiles and amphibians,
primarily frogs and snakes, are consumed (Toweill and Tabor 1982, Melquist and Hornocker
1983). Turtles are somewhat rare food items, but are taken on occasion (Toweill and Tabor 1982,
Ligon and Reasor 2007).
Avian prey is important to otters in some locations. Waterfowl and rails (Rallus sp.) are preyed
upon with some regularity (Knudsen and Hale 1968, Lauhachinda 1978) and may represent an
unknown proportion of hunter-crippled birds or carrion. However, there have been observations
of otters actively hunting and killing healthy birds (Cahn 1937, Meyerriecks 1963). Otters have
been known to prey on chicks in coastal nest colonies with serious impacts (Verbeek and
Morgan 1978, Speich and Pitman 1984).
A variety of mammals have been reported in the otter diet, but occurrence is uniformly low.
Field (1970) presented evidence of otters actively hunting and capturing small mammals in the
snow up to the size of a snowshoe hare. Otter predation on other furbearers is extremely
uncommon (Toweill and Tabor 1982). Muskrats have been reported as food items, but contribute
little to the otter diet (Wilson 1954, Melquist and Hornocker 1983). Otter predation on beavers
has been reported (Green 1932). However, scat analysis and recent studies show that beavers are
12not eaten by otters (Larsen 1983, Melquist and Hornocker 1983). Simultaneous use of a beaver
lodge by both beavers and otters has been documented (Melquist and Hornocker 1983).
Small proportions of freshwater mussels, periwinkles, clams, and snails occur in the otter’s diet,
but are apparently not important (Toweill and Tabor 1982). Likewise, a wide variety of insects
have been recorded in food habit studies. However, the occurrence of insects in scats or digestive
tracts may be part of fish gut remains, since insects are a staple in fish diets (Toweill and Tabor
1982). Plant parts such as blueberries (Vaccinium sp.) and rose hips (Rosa sp.) have been
reported (Toweill and Tabor 1982).
River otters have high metabolic rates as compared to other land mammals (Iversen 1972) and
have efficient digestive systems. Liers (1951) found that otters previously fed bland foods passed
exoskeletal remains of crawfish in about 1 hour after feeding.
Otters typically forage by diving and catching fish or digging in pond or stream substrate.
Melquist et al. (2003) described otter foraging behavior in a variety of aquatic habitats. In
shallow streams, fish are forced to seek shelter along the shoreline to avoid potential predation.
Undercut banks, along submerged logs, overhanging vegetation, and other obstructions provide
escape cover for fish. In exposed areas, fish quickly retreat to shelter when an otter is present and
often get captured. In larger streams, otters forage in areas where fish tend to congregate such as
in deep pools, logjams, and slow-moving stream sections. Otters in lakes forage along the
shoreline or among boat docks. In shallow lakes and ponds, otters feed along the shoreline and
capture fish by direct pursuit.
During foraging behavior observation, Melquist and Hornocker (1983) reported no evidence of
cooperative hunting among otters. Beckel (1990) observed group foraging, but saw no
coordinated hunting strategy. Serfass (1995) observed a group of four otters, believed to be an
otter family, herd fish in a stream into the center of a pool and successfully catch two fish. He
believed that this foraging behavior was a result of juvenile otters transitioning from their
dependence on the female for acquiring food.
Hunting success rates of otters is poorly documented. Varley (1998) conducted a study in
Yellowstone National Park and observed two female otter successfully catching fish during 37-
40% of their dives in a lake. One of the otters was successful during 62% of her dives in an inlet.
Social organization, spatial distribution, and behavior
The basic river otter social group is the family unit consisting of an adult female and her juvenile
offspring. Adult females spend a considerable amount of time teaching vital survival skills to
pups. Social relations beyond the family group are generally uncommon. Unrelated otters
typically show mutual avoidance (Melquist and Hornocker 1983). Adult males are not associated
with the family group and are normally solitary.
Where food is abundant, river otters may form social groups as part of cooperative foraging in
coastal areas (Blundell et al. 2002). The family unit may include one or more helpers, who may
be members of a previous litter or an unrelated individual (Rock et al. 1994). Shannon (1998)
13defined another social group called a clan. Composed primarily of males, clans consisting of 9-
30 otters have been reported as part of cooperative foraging in marine environments (Woolington
1984, Shannon 1989, 1991, Reid et al. 1994, Rock et al. 1994, Testa et al. 1994). Females are
thought to avoid joining foraging groups because of the time-consuming task of raising young
(Blundell et al. 2002).
River otters are intelligent, quick, highly active, and inquisitive. Their reputation for play
behavior is unmatched. In captivity, they often engage in repetitive actions such as sliding,
wrestling, and retrieving or juggling inanimate objects from underwater. Play behavior is poorly
documented for wild otters. Only 6% of field observations of free-ranging otters in Idaho showed
play behavior and was usually associated with immature individuals, primarily juveniles
(Melquist and Hornocker 1983). Playfulness may primarily be displacement behavioral in
response to captive conditions (Melquist et al. 2003). Sliding over snow and ice as a means of
efficient travel is common among otters. However, mud and snow slides created by repetitive use
during play are rare (Mowbray et al. 1979, Melquist and Hornocker 1983).
Otters regularly communicate using their sense of smell. Olfactory communication through scent
marking with feces, urine, and anal gland secretions play a significant role in intergroup
communication. Scent markings apparently do not function as territorial boundaries, but are a
means of advertising the presence of individuals or groups, minimizing intraspecific contact
(Hornocker et al. 1983). Scent posts are maintained throughout an otter’s range. Scent posts are
1-2 m2 areas of digging and scratching without evidence of food remains, scats, or beds
(Mowbray et al. 1979). Otter latrines are specific sites for defecation purposes used on a regular
basis (Greer 1955). However, single scats may be deposited near scent posts, rolling areas, or
structures such as logs extending into the water (Melquist and Hornocker 1979).
Otter latrine sites at or near the shoreline are somewhat prominently displayed and often consist
of new and old scats that are tubular or patty-like in shape. Fresh scats are often surrounded with
a jelly-like, intestinal substance. Recent scats reek of strong fish odor. Old scats often
disintegrate into piles of fish scales or crawfish remains. Large rocks or waterway banks
bordering deep water are common latrine locations. Otters will often roll in vegetation, then
urinate and defecate on it as part of territorial marking. The same latrine sites may be used year
after year.
River otters are generally nocturnal or crepuscular. Early morning activity is very common
among otters throughout their range. The peak of feeding activity occurs from dawn to mid-
morning (Toweill and Tabor 1982). Diurnal activity is not uncommon. Individual differences
among otters and disturbance sources such as human activity may cause variations in activity
patterns (Melquist and Hornocker 1983). Unlike most predators, otters do not have to
synchronize foraging with prey activity. They have access to aquatic prey throughout the day and
night. Melquist and Hornocker (1983) recorded greatest daily movements of family groups of
otters in Idaho during the spring following snow melt and least movement during the winter
when many small tributaries and ponds were covered with ice and snow.
14Daily movements of single otters and family groups tend to be < 6.2 mi (10 km), but vary by
season. Dispersing otters are highly mobile with recorded 1-day distances of up to 26 mi (42
km)(Melquist and Hornocker 1983).
A home range consists of the area where an animal lives, reproduces, and satisfies all of its life
requirements. The shape and size of river otter home ranges depend on the distribution of
suitable habitat and available food as well as on weather, topography, density, reproductive
status, and season of the year (Melquist et al. 2003). Within a home range, activity is
concentrated at one or more sites supplying abundant food and cover (Melquist and Hornocker
1983). Age and gender classes show varied home range sizes. Males have larger home ranges
than females. Lactating females have the smallest home ranges (Melquist and Hornocker 1983).
Home range overlap is very common, but mutual avoidance is typically practiced. River otters do
not defend territories, but exhibit very flexible spacing strategies (Hornocker et al. 1983).
Home range sizes and densities throughout North America have been estimated using multiple
methods, sample sizes, and age and gender groups making comparisons difficult (Table 1). The
distribution of adequate food and shelter differ among regions. Linear and two-dimensional
home ranges are also difficult to compare. Strong site attachment for activity centers which often
determines seasonal home range limits may be the primary reason for the existence of otter home
ranges (Melquist and Hornocker 1983).
Table 1. Home range and density estimates of river otters in North America.
State or
Home range estimate Density estimate Source
province
Alaska 19-40 km; 9-25 km2 1 otter/ 1.9-2.1 km Larsen (1983)
1-23 km 1 otter/ 1.2 km Woolington (1984)
20-40 km 1 otter/0.2-0.8 km Testa et al. (1994)
Bowyer et al. (1995)
Alberta n/a 1 otter/ 10-17 km Reid (1984)
2
Colorado 29-57 km n/a Mack (1985)
Idaho 8-78 km 1 otter/ 3.9 km Melquist and Hornocker (1983)
Missouri 4-9 km2 1 otter/ 4.0 km2 Erickson et al. (1984)
11-78 km 1 otter/ 8.0 km Erickson et al. (1984)
2 2
Texas 2-5 km 1 otter/ 0.7-1.1 km Foy (1984)
Otter population densities vary according to habitat suitability. The most dense otter populations
occur in the least disturbed, food-rich coastal marshes and estuaries.
Habitat
River otters are able to adapt to diverse aquatic habitats. Their presence is an indicator of high
quality watercourses. The availability of food, shelter, and water determines the duration and
intensity of habitat use. In inland habitats, otters frequent lowland marshes and swamps
interconnected with meandering streams and small lakes (Melquist and Hornocker 1983). Otters
15may be common in the tributaries of major unpolluted watersheds with minimal human impact,
but may be scarce in highly-disturbed and polluted watercourses (Melquist and Dronkert 1987)
or in mountain streams with limited food resources (Melquist et al. 2003). Water altered by acid
mine drainages do not support otters, nor their prey. During otter restoration in western
Pennsylvania during 1993, acid mine pollution postponed reintroduction efforts in parts of the
Youghiogheny River watershed. A blow-out of a deep mine contaminated the Casselman River,
a feeder of the Youghiogheny River (Kosack 1995).
Adequate food is a key habitat component that influences otter habitat use considerably. Habitat
that supports otter prey species is important. Logjams, fallen or partially-submerged trees, and
other shallow water structures often provide abundant food, adequate shelter, and minimal
disturbance. These types of areas have been referred to as activity centers because of their high
frequency of use (Melquist and Hornocker 1983).
Other key habitat components are temporary dens and resting sites. Sheltered sites that provide
protection and seclusion are preferred. However, otters select these sites according to availability
and convenience (Melquist and Hornocker 1983). Beavers create important den sites as well as
foraging areas for otters. The strong relationship between beaver habitat and use by otters has
been well documented (Choromanski and Fritzell 1982, Melquist and Hornocker 1983, Reid
1984, Reid et al. 1994, Swimley et al. 1999). In Idaho, Melquist and Hornocker (1983) found
that 15 radio-marked otters used active and abandoned beaver bank dens more (32%) for den and
resting sites than any other site category. Beaver stick lodges accounted for 6% of selected den
or resting sites. Logjams (18%) and riparian vegetation (11%) were also frequently used. They
also found that dispersing otters often rested in dense riparian vegetation and snow or ice
cavities. They surmised that these individuals were probably unfamiliar with the location of more
suitable resting sites or because no more suitable site was available.
Two key habitat needs, availability of prey and shelter, are largely satisfied by beaver ponds.
LeBlanc et al. (2007) found otter activity at beaver ponds positively associated with beaver
presence, pond size, and vegetation cover in New Brunswick, Canada. They found that the
dynamics of beaver pond succession (pond creation, expansion, and abandonment) created a
mosaic of ponds that ultimately influenced the river otter’s own pattern of habitat use and
distribution.
Riparian vegetation along streams, rivers, lakes, and other wetland areas is a key component of
otter habitat. Cavities along tree roots, dense shrubs, and tall grass provide escape cover and
temporary resting sites. The habitat conditions created by adequate riparian vegetation and
structure increase the likelihood that an area will be used (Melquist and Dronkert 1987). Otters
tend to avoid watercourses with gradually-sloping shorelines of sand and gravel, such as water
storage reservoirs (Melquist and Hornocker 1983, Reid et al. 1994). Bare shorelines lack escape
cover and den and resting sites for otters. Structural diversity of shorelines tends to increase
escape cover for prey species and makes them more available to otters (Allen 1987).
16SECTION 2: HISTORIC AND CURRENT STATUS IN PENNSYLVANIA
Historic status
River otter bones were commonly found in prehistoric Native American village sites throughout
Pennsylvania (Doutt et al. 1977). Otters historically occurred in every major watershed
statewide. During 1894, Rhoads (1903) reported viable otter populations in the heavy-populated
counties of Chester, Delaware, Philadelphia, and Bucks as well as unpolluted glacial lakes and
tidewater streams. Unlike beavers, wolves, and panthers, he believed otters escaped extirpation
because of their nocturnal activity patterns and extreme wariness.
The combined effects of habitat destruction, water pollution, and unregulated harvest caused the
extirpation of river otters from most of Pennsylvania by the early to mid-1900s. Noxious stream
conditions were produced by drainage from tanneries, mines, oil wells, chemical works,
factories, and foundries beginning in the 1800s (Rhoads 1903). Deteriorating water quality
quickly eliminated fish and other aquatic life from Pennsylvania’s waterways. The last recorded
otter in the Allegheny River was in 1899; the last in Pymatuning Swamp was in 1908 (Doutt et
al. 1977). In 1952, the Pennsylvania Game Commission (PGC) closed otter trapping season.
River otters were never completely extirpated from Pennsylvania. The Pocono region always
supported otters, especially the counties of Wayne, Pike, and Monroe (Doutt et al. 1977; Eveland
1978).
Population recovery
Nationwide, 21 states implemented river otter reintroduction projects during 1976-1998,
releasing 4,018 river otters (Raesly 2001). Based on various forms of direct and circumstantial
evidence, Raesly (2001) found that most reintroductions were considered successful in restoring
extirpated otter populations.
During 1982-2004, the Pennsylvania River Otter Reintroduction Project, headed by Dr. Thomas
Serfass, established stable, self-sustaining river otter populations in Pennsylvania. The program
reintroduced 153 river otters successfully to eight water systems in central and western
Pennsylvania (Fig. 2). The effort was comprised of five developmental and implemental stages:
1) site selection, 2) identification and selection of appropriate sources and numbers of animals, 3)
veterinary care, captive management, and translocation, 4) public relations and education, and 5)
post-translocation monitoring and evaluation (Serfass et al. 1993, Hubbard and Serfass 2004). A
successful, ecologically-based, and publicly-supported reintroduction project resulted from the
carefully planned effort.
States conducting reintroduction projects obtained otters from a variety of sources. Raesly (2001)
surveyed state agency biologists and found that most (64%) states released at least some otters
originating from coastal Louisiana as part of their reintroduction programs. In Pennsylvania,
released otters originated from Louisiana, Maryland, Michigan, New Hampshire, New Jersey,
New York, and the native Pennsylvania population (Serfass et al. 1993).
17Allegheny
River
Tionesta Kettle Loyalsock
(22)
Creek Creek Pine Creek Creek
(28) (4) (22) (13)
1980
Native
Population
Youghiogheny Laurel Hill Raystown Branch/
River Creek Juniata River
(28) (13) (23)
Fig. 2. Pennsylvania river otter reintroduction sites and number of otters released (in
parentheses) during 1982-2004.
Pennsylvania’s otter population has been protected and growing for over 30 years after otter
restoration was initiated. Restoration efforts, range expansion of native population, and influx
from Ohio, New York, and Maryland restoration efforts lead to successful population recovery.
Population monitoring
We currently use a combination of population indices such as accidental capture frequency and
local status and distribution field surveys to monitor otter populations. Since no harvest season
for otters exists in Pennsylvania, mortality information is collected from records of accidental
captures, highway accidents, and mortalities resulting from damage control and illegal take.
Based on records of 211 otter carcasses collected during 1996-2009, most reported mortality was
a result of accidental captures (69%) and highway accidents (24%)(Fig. 3). A very small
proportion (2%) of otter mortality was attributed to damage control measures and illegal take.
As river otter populations expanded throughout the Commonwealth, reports of accidental otter
captures have steadily increased. Otters are typically captured in foothold or body-gripping traps
set for raccoons or beavers. Some are released at the capture site by trappers or local wildlife
18conservation officers. Otter mortalities usually associated with body-gripping sets occur
occasionally during beaver trapping and are not always avoidable.
Damage Illegal
1% 1%
Unknown
5%
Roadkills
24%
Accidental
captures
69%
Fig. 3. Causes of river otter mortality during 1996-2009 in Pennsylvania (n=211).
Reports of accidental otter captures provide annual trends in relative density and distribution.
Two independent survey mechanisms, the annual Furtaker Survey (Appendix 1) and the annual
Wildlife Conservation Officer furbearer questionnaire (Appendix 2), are currently used to
monitor accidental otter captures. These techniques are not designed to provide complete counts
of these captures, but rather to monitor temporal trends in otter abundance and distribution.
The annual Furtaker Survey is a mail questionnaire sent to approximately 20% of licensed
furtakers to assess harvest levels for various furbearers. Furtakers are asked to report the number
and WMU locations of otters captured incidentally in traps set for other furbearers. There has
been a general increase in the numbers of otters captured during the past 5 years (Table 2). If the
number of otters captured per trapper is extrapolated to include all furtakers, the estimated
number of captured otters averages 138 each year during the 2007-2011 furtaker seasons.
WMU 3C, located in the northeast corner of PA within sustained otter range, has the greatest
number of incidental captures, averaging 37 each year (Fig. 4). Trappers in the northwestern
WMUs, 1B and 2F, consistently catch an estimated average of 16 and 14 incidental otter each
year, respectively. In central Pennsylvania, trappers sporadically catch incidental otters from
WMUs 4D and 4E. The estimated mean incidental catch is 11 otters annually from these units.
Lesser and more sporadic incidental otter captures occur in the remaining WMUs.
19Table 2. Estimated number of river otters captured during the past 5 trapping seasons based
on mail surveys sent to approximately 20% of licensed furtakers.
Otter captures
Survey Estimated total
Season Furtakers reported by survey
Annual River Otter Incidental Captures
2007-08
respondents
2,994 28,033
respondents
7
otter captures
66
2007-2011 Seasons
2008-09
2009-10
2,622
3,186
29,717
31,110
12
14
136
137
2010-11 4,421 35,267 24 191
Average Annual River Otter Incidental Captures
2011-12 3,609 36,187 16 160
2007-2011 Seasons
1B 3A
3C Incidental
2F river otter
2H 3B
2G captures
Otter incidental
1A 3D per year
captures
0
2D 4E 0
2E 4D 2-3
4C 6 -2
8 -3
11 - 16
2B 4B 5C 6 -8
37
11 - 16
2C 4A 5B 5D
2A 5A 37
Fig. 4. Spatial distribution of the average number of river otter incidental captures per year
during 2007-2012 among WMUs, estimated from Furtaker mail survey results.
Furbearer questionnaires are mailed annually to all Wildlife Conservation Officers (WCOs) to
collect a variety of furbearer information. Accidental captures of otters during the previous
calendar year were reported by WCOs via this survey. This second measure of otter accidental
captures shows an increasing linear trend during 1995-2011 (Fig. 5). There was little or no
change in beaver trapping effort during the same period. Numbers of accidental otter captures,
primarily by beaver trappers, have increased with greater than 25 captures reported annually
since 1996 (Fig. 5).
Starting in 2001, we attempted to minimize incidental captures of river otters by publishing
capture avoidance guidelines in our Hunting and Trapping Digest. Body-gripping trap trigger
configurations, snare loop sizes, and trap site locations to avoid otter captures were key topics
covered in this attempt to change beaver trapline habits. This educational effort likely reduced
incidental otter captures. We believe that the increasing trend in incidental otter captures
depicted in Figure 5 relates more to otter range expansion and increasing population density than
20to any other factor. We expect the trend in incidental otter captures to stabilize or slightly
increase as the use of otter capture avoidance techniques are used more widely.
R=0.81
Fig. 5. Statewide river otter accidental captures recorded by Wildlife Conservation Officers in
annual furbearer questionnaires. Incidental capture information was not collected during 2002.
Current status and distribution
As part of WCO furbearer surveys, we annually ask WCOs to report the status of otter
populations within their local districts. In 1995, otters were absent in 51% of WCO districts. In
2011, otters were absent in only 10% of WCO districts. The maps in Figure 6 depict the change
in otter distribution and population status during 1995 and 2010 within 137 Pennsylvania WCO
districts. The solid blue areas represent occupied river otter range in Figure 6. In 1995, otters
ranged over 49% of WCO districts. In 2010, otters occurred within 87% of WCO districts.
1995 2010
Otter
population
Otter
status
Otter
population
status
population
status
Increasing
Stable
Increasing Increasing
Present/Stable
Absent
No data
Present/Stable Absent
No data
Absent
No data
Fig. 6. Pennsylvania river otter distribution and population status in 1995 and 2010 based on surveys of
Wildlife Conservation Officers. Subdivisions represent Wildlife Conservation Officer district boundaries.
During 2010, field officers reported that otter populations were well established throughout
Pennsylvania except for scattered WCO districts primarily in the southern half of Pennsylvania.
21All data suggest that otter populations are currently increasing in density and expanding
geographically throughout Pennsylvania. Otter populations occupy all major river systems.
The Delaware, Susquehanna, Allegheny, and Youghiogheny Rivers support sustained otter
populations and act as travel corridors from which new populations disperse and expand
geographically. The Potomac and Lake Erie watersheds maintain less dense populations, but
continue to increase in otter numbers annually.
22SECTION 3: RESOURCE AND ECONOMIC VALUES
Resource value
River otters have been an economically important furbearer species since the Europeans first
arrived in North America. Over 11,000 otter pelts were shipped from Canada to London by the
Hudson Bay Company in 1873 (Rhoads 1903). Fur values at the turn of the twentieth century ran
as high as $10-12 per pelt (Rhoads 1903). During the fur boom in the 1920s, otter pelts sold for
an average of $31 (Deems and Pursley 1983). Market values decreased during subsequent
decades, and generally followed inflation rates thereafter. Annual harvest reached about 50,000
pelts during the late 1970s (Deems and Pursley 1978). Higher harvest totals appeared to correlate
with higher pelt prices.
The value of regulated river otter trapping as an outdoor activity and tradition is difficult to
quantify. For most trappers, there is no single motive driving their participation. Recreation,
challenge, outdoor experience, and similarly-phrased reasons are identified as primary
motivators (Bailey 1981, Boddicker 1981, Marshall 1981, Samuel and Bammel 1981). Income
from trapping is less important to trappers, but fur values profoundly affect trapper numbers,
trapping effort, and harvest for most furbearer species (Erickson and Sampson 1978, Erickson
1981).
Over the years, otter pelts have been and continue to be widely used in the garment industry. Use
of otter pelts varies from natural long hair to sheared and dyed garments (Ethier 2003). When
plucked, otter pelts are never sheared (Schipper 1987). Fashions are unpredictable, but drive the
world demand for pelts. World markets for otter pelts frequently fluctuate and correspondingly
change the price paid for pelts at local markets. Proper pelt handling and preparation as well as
pelt primeness, size, and characteristics determine prices paid.
Due to new technologies in the dressing process and new world markets, otter pelts tend to bring
a higher dollar value now than in the recent past. Northeastern states and Canadian provinces
reported otter pelt prices averaging $60.68 over the past 5 years and $67.82 over the past 10
years (Northeast Furbearer Resources Technical Committee, pers. commun., 2012). River otter
pelts sold for an average of $86.34 at the January 2013 Fur Harvesters Auction in North Bay,
Ontario. Prices are expected to hold at current levels or increase.
Because otter have specialized requirements and are large in size, raising them in captivity on a
fur farm was never a profitable venture (Toweill and Tabor 1982). Some individuals in parts of
Europe and Asia maintain otters as pets, but this practice never became popular in North
America.
Damage management
River otters may cause severe depredation problems in and around fish hatcheries. Serfass et al.
(1990) found that 10 of 21 fish hatcheries surveyed in Pennsylvania experienced losses due to
otter depredation. Small farm ponds and other confined watercourses supporting high densities
of fish are most susceptible to predation problems. In isolated cases, economic loss can be
23You can also read
